Types of Texture Projection

Choosing the right type of texture projection is an important part of the texturing process. The more closely the projection conforms to the shape of the object, the less you’ll have to adjust the texture to get the object looking just right. This section describes the types of texture projection that are available to you:

Planar Projections

Cylindrical Projection

Spherical Projection

Cylindrical Projection

Spherical Projection

Lollipop Projection

UV Projection (NURBS Surfaces Only)

Camera Projections

Cubic Projections

Spatial Projection

Unique UVs Projection (Polygons Only)

Contour Stretch UVs Projection (Polygons Only)

Unfold Projection

Planar Projections

Planar projections project a texture along an axis onto the specified plane.

 

Planar XY, XZ, and YZ projections

Cylindrical Projection

Cylindrical projections project a texture from a virtual cylinder around an object toward the central axis of the cylinder.

 

Spherical Projection

Spherical projections map a texture onto an object similarly to a beachball, with some distortion at the +Y and -Y poles.

 

Lollipop Projection

A lollipop projections wraps the texture around the top of an object, with the corners meeting at the bottom like the wrapper of a lollipop. To apply a lollipop projection, you must use the TextureWizard as described in Using the TextureWizard.

 

UV Projection (NURBS Surfaces Only)

UV projections follow the UV parameterization of NURBS surface objects (no relation to texture UV coordinates). A UV projection behaves like a rubber skin stretched over the object’s surface. The points of the object correspond exactly to a particular coordinate in the texture, allowing you to accurately map a texture to the object’s geometry.

 

Reparameterizing a UV surface will affect the UV projection as well, depending on the projection’s position in the operator stack. See Controlling Whether Textures Stick or Swim.

 

A NURBS surface with a wood texture applied using an planar XZ map and UV map. With the UV map applied, the pattern accurately follows the contours of the object.

A

NURBS surface

B

Texture image used

C

Planar XZ projection

D

UV projection

Camera Projections

A camera projection projects a texture from the camera onto the object’s surface, much like a slide projector does. This is useful for projecting live action backgrounds into your scene so you can model and animate your 3D elements against them.

Changing the camera’s position changes the projection’s position. Once you have positioned the texture on the surface to your liking, you can freeze the projection.

 

The corner of a room was textured using a texture image that was projected from a scene camera. The rendered result shows the modeled teddy bear against the projected background.

A

Texture image used

B

Wireframe view of the rendered frame

C

Top view showing where the texture is projected

D

Final rendered frame

 

Camera projections store the distance to the camera in the W component of texture UVW coordinates. This value is not updated after the projection is frozen. This can cause texturing discontinuities if you modify topology after freezing the projection.

Applying a Camera Projection

1. Do one of the following:

- Select the elements to texture (one or more objects, groups, hierarchies, polygons, or polygon clusters) and then choose Get > Property > Texture Projection > Camera Projection from any toolbar.

or

- In a texture shader’s property editor, choose New > Camera Projection in the Texture Projection group box.

or

- In a texture shader’s property editor, choose New > Create New Projection in the Texture Projection group box, then set Projection Type to Camera in the TextureWizard and click OK.

2. Pick a camera object.

3. Navigate the camera or transform the objects in the scene so that the texture fits properly. You can use the render region in the camera view to verify the rendered result.

Once the projection is to your liking, you can freeze the projection to stop the texture from following the camera when it moves. For more information about freezing texture projections, see Freezing Texture Projections.

Cubic Projections

When you apply a cubic projection to an object, the object’s faces are assigned to a specific face of a cubic texture support, based either on the orientation of their polygon normals or their proximity to a face. The texture is then projected from each face of the support using a planar or spherical projection method.

By default, the entire texture is projected from each of the cube’s six faces. However, you can choose from a number of different cubic projection presets. You can also transform each face of the cube individually and save the transformations as presets of your own.

 

A cubic projection is applied to a head (B) so that a different part of the texture image (A) is projected onto each face. In this case the preset used was Cubic_verticalcross.

Applying a Cubic Projection

1. Do one of the following:

- Select the elements to texture (one or more objects, groups, hierarchies, polygons, or polygon clusters) and then choose Get > Property > Texture Projection > Cubic from any toolbar.

or

- In a texture shader’s property editor, choose New > Cubic in the Texture Projection group box, and then click Edit.

or

- In a texture shader’s property editor, choose New > Create New Projection in the Texture Projection group box, then set Projection Type to Camera in the TextureWizard and click OK. Finally, click Edit in the Texture Projection group box.

2. By default, the entire texture is projected from each of the cube’s six faces. If that’s not what you want, the first thing is to select a different configuration. Do one of the following:

- On the Layout tab, click one of the Preset icons.

or

- On the Layout tab, click Load Preset and select a saved preset from the browser.

or

- On the Custom tab, configure each of the cube’s faces independently. If desired, you can save a preset of your custom configuration by clicking Save Preset on the Layout tab.

3. Set the other options as desired, in particular Face Selection and Face Projection. For a description of all options, see Texture Support Property Editor [Properties Reference].

Spatial Projection

A spatial projection is a three-dimensional UVW texture projection that projects through an object’s volume. It is typically used with procedural 3D textures for materials that have internal structure like wood, marble, and so on. If you deform the object or transform the texture support relative to the object, different parts of the internal texture are revealed.

 

The texture support for the vein texture was translated slightly to the right, showing how the veins change shape, merge, and diverge internally.

 

When you open scenes from older versions of Autodesk Softimage, you’ll notice that spatial projections have no texture support. In such cases, you can still have the projection computed in world space by doing the following:

1. Select the object and open an explorer.

2. Locate the GeoTxtOp operator (under the object’s Texture Projection node) and click its icon to open its property editor.

3. Activate the Compute in World Space option.

Unique UVs Projection (Polygons Only)

Unique UVs mapping applies a texture to polygon mesh objects using one of two possible methods:

Individual polygon packing assigns each polygon’s UV coordinates to its own distinct piece of the texture so that no one polygon’s coordinates overlap another’s.

This is useful for rendermapping polygon meshes. Typically, you apply textures to an object using a projection type appropriate to its geometry. Then you can rendermap the object using a new Unique UVs projection to output a texture image that you can reapply to the object. The texture is applied to texture each polygon properly without you worrying about “unfolding” it to fit properly.

A polygon-packing style Unique UVs projection only produces good results if you use a texture created specifically for the projection, for example, an image created using Render Map.

Angle Grouping, after deciding on a projection direction, groups together neighboring polygons whose normal directions fall within a specified angle tolerance. This process is repeated until all of the object’s polygons are in a group. The groups — or islandsare then assigned to distinct pieces of the texture so that no two islands’ coordinates overlap each other.

 

The result of a Unique UVs projection is different on 32-bit and 64-bit systems. To avoid problems when opening a scene on a different operating system, freeze the projection first — see Freezing Texture Projections.

 

A

A Unique UVs projection was applied to this sphere.

B

The Individual Polygon Packing method produces UV coordinates that look like this: each polygon’s UV coordinates separated from the rest of the coordinate set so it can be assigned to its own portion of texture.

C

The Angle Grouping method produces “islands” of polygons.

Contour Stretch UVs Projection (Polygons Only)

Contour Stretch UVs projections allow you to project a texture image onto a selection of an object’s polygons. Rather than projecting according to a specific form, a contour stretch projection analyzes a four-cornered selection to determine how best to stretch the polygons’ UV coordinates over the image.

Contour stretch projections do not have the same alignment and positioning options as other projections. Instead, you select a stretching method that is appropriate to the selection’s topology and complexity. Also, contour stretch projections do not have a texture support. You can adjust them only from the texture editor.

Contour stretch projections are useful for a number of different texturing tasks, particularly for applying textures to tracks and roads on irregular, terrain-like meshes. They are also useful for fitting regular-shaped textures onto curved meshes. For example, they would be useful to place a label texture on a beer bottle, right at the junction of the bottle’s neck and body.

 

A

Original object. The contour stretch projection is ideal for texturing the curvy path on the top of the object.

B

First the polygons on top of the object are selected and a Contour Stretch UVs projection is applied.

C

A pick session allows you to define new corners for the initial polygon selection if necessary.

D

Once the pick session ends, the projection is applied. Since no texture is applied yet, the default texture is used.

E

Applying a texture using the contour stretch projection applies the texture to the polygon selection. As you can see, it needs some adjustment.

F

Adjusting the Contour Stretch UVs projection’s properties realigns the projection’s UV coordinates so that the texture is placed correctly.

Although the easiest geometry to contour stretch is a rectangular grid of quads, it’s more likely that you’ll want to use contour stretch projections on less regular shapes. This is not a problem as long as you keep a few simple guidelines in mind when you make your selection.

• The selection cannot be a whole object: it must be a selection of polygons with an identifiable contour.

• Although the selection doesn’t have to be perfectly rectangular, the contour stretch projection must be able to derive four corners from its contour.

• If the selection has holes in it, it is more likely to produce undesirable results.

• If the selection consists of two or more discontiguous “islands,” their UV coordinates do not remain separated in the texture editor once the projection is applied. Instead, they are treated as a single, one-piece selection.

Applying a Contour Stretch UVs Projection

1. Select any number of polygons on the object to which you want to apply the contour stretch projection.

Remember that the selection must have four discernible corners (even if it isn’t perfectly rectangular) and a clear contour.

2. From the Render toolbar, choose Get > Property > Texture Projection > Contour Stretch UVs.

The selection’s corners are automatically detected, the object’s points are displayed, and a pick session begins.

3. Do one of the following:

- If necessary, pick new corners for the polygon selection to which you are applying the projection. The new corners must lie on the boundary of the initial polygon selection. Then right-click to end the pick session.

or

- Right-click to end the pick session and use the automatically detected corners.

Three things happen:

- An internal cluster, which is neither visible nor selectable, is created from the initial polygon selection.

- The contour stretch projection is applied to the cluster.

- The PolyUVContourStretching property editor opens.

4. Choose a contour stretch method and set any other options as desired. See Poly UV Contour Stretching Property Editor [Properties Reference].

 

Once you’ve applied a contour stretch projection, modifying any of the topology changes that you made before applying it will have dramatic and usually undesirable results. This is because the topology change affects the contour that the projection uses to stretch the polygon selection.

Unfold Projection

Unfolding creates a UV texture projection by “unwrapping” a polygon mesh object using the edges you specify as cut lines or seams. When unfolding, the cut lines are treated as if they are disconnected to create borders or separate islands in the texture projection. The result is like peeling an orange or a banana and laying the skin out flat.

 

Unfolding a Texture Projection

1. Select a polygon mesh object.

If desired, you can also select edges to use as cut lines (remember to click Add to Cut Line in step 3). Whether or not you select edges now, you can still add and remove cut lines later in the procedure.

2. Choose Get > Property > Texture Projection > Unfold.

An Unfold property is applied to the mesh and its property editor opens. For a description of all the options in this property editor, see Unfold Property Editor [Properties Reference].

3. Define the edges to use as cut lines:

- Select some edges and click Add to Cut Line. Repeat to add more edges.

- If you added some edges that you don’t want, select them and click Remove from Cut Line.

- To start over with a completely new set of edges, select the desired edges and click Set from Current Edges.

- To see the edges that are currently set as cut lines at any time, click Select Cut Line.

For some tips, see Tips for Choosing Cut Lines.

4. When you have set the desired cut lines, click Unfold and Pack.

5. Open the texture editor (Alt+7) or refresh it to see the result of the unfolding. Note that if the object already had a UV texture projection, then you may need to select the Unfold projection from the UVs menu.

6. If desired, you can continue to adjust the cut lines as in step 3. Click Update and Pack or Update No Pack to see the results in the texture editor.

If you want to concentrate on one or more islands at a time, then you can re-unfold those specific islands without affecting others. In the texture editor, select the desired islands and choose Tools > Re-Unfold Selected Islands (Unfold Op Only). This command works only if you have used this procedure to unfold the mesh, that is, if there is an Unfold operator in its texture projection stack.

7. Use the Texture Editor - Adjust Unfold options to reduce the amount of surface stretching (at the expense of distorting the edge angles). Click Adjust to modify the unfolding in the texture editor with the specified Iterations and Stretching values. The effect is cumulative — each time you click Adjust, another operator is added to the texture projection stack. If you want to experiment with different settings, make sure to undo between each set of values.

8. If desired, use the options on the Packing tab to control how the UV islands are laid out in UV space. You can either set these options and then click Pack, or activate Live packing to see the effects as you make changes.

Alternatively, you can pack manually by translating the islands in the texture editor. However, any other type of manual change will be lost if you update the unfolding.

9. If you need to make changes later, you can re-open the Unfold property from an explorer:

 

If you are completely satisfied with the unfolding and certain that you will never need to change it, you can freeze the texture projection.

Tips for Choosing Cut Lines

The principal goal for choosing cut lines is to minimize the amount of distortion when the mesh is flattened out. For example, if you simply flatten an open cylinder, there is an undesirable distortion in the size of the polygons.

 

 

In addition, you should try to minimize the number of islands and the lengths of the cut lines as much as possible. This results in less work for the texture painter when smoothing the change of color across the seams. You should also try to place cut lines where they will be less visible, for example, under the arms or behind the head, so that any problems at the seams will be less noticeable.

Here are some general guidelines for minimizing distortion. However, the final choice of cut lines depends greatly on the shape of the specific object.

• For tube-shaped islands, add a cut line along the length.

 

 

• For conical islands, add a cut line from the tip to closest boundary.

 

 

• For sock-shaped islands, add a cut line along the length with a partially detached “cap”.

 

 

• Holes in islands can sometimes cause distortions. If this occurs, try splitting the islands to remove the holes.

Some shapes cannot be unfolded well without being cut into many islands. For example:

• Cubical objects likely need a separate island for each side.

• Man-made objects that are composed of multiple box-like parts, like buildings, furniture, automobiles, and so on, will likely require many separate islands to unfold well.

Freezing Unfold Projections

The Freeze M button (freeze modeling) does not freeze the Unfold operator in the texture projection stack. To freeze it, do either of the following:

• Select the Unfold projection or UnfoldOperator in the projection stack (not the Unfold custom property) in an explorer and click Freeze. For more information, see Freezing Texture Projections.

or

• In the texture editor, choose Edit > Freeze.

Freezing the Unfold operator does not remove the Unfold custom property on the object. If the operator has been frozen, then using the buttons in the Unfold property editor will create a new set of UV coordinates.

 



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